Optical TE-TM mode splitters are important optical devices, so far, various guided-wave TE-TM mode splitters have been demonstrated or modeled. Those splitters can be divided into two groups. One uses the optical interference in a directional coupler. The TE and TM modes of a the coupler can be split by the difference of their coupling lengths. However, this type mode splitter needs a very careful design to achieve a high extinction ratio. It has low fabrication tolerance, and can only be operated under single-mode condition. The other uses an asymmetrical Y-junction structure. The incident TE and TM modes are split by two output arms due to their different preferences of polarization. In practical application, those which use the Y-branch have a larger fabrication tolerance. But the fabricated device is fundamentally based on the adiabatic mode conversion of the extraordinary-polarized mode. A careful design of the waveguide pattern for a specific index distribution is then required to obtain a maximum extinction ratio. To our knowledge, an ideal TE and TM mode splitter, in which each branching waveguide supports only a single-polarized wave (TE or TM), has not been demonstrated.
Therefore, an object of the present invention is to provide a new TE-TM mode splitter, which has a high fabrication tolerance, a high extinction ratio and is capable of operating within a wide range of wavelength, either single mode or multimode.